Purification of beet sugar solutions



Jan. 24, 1961 R. A. M GINNIS PURIFICATION OF BEET SUGAR SOLUTIONS Filed June 22, 1959 .Wce

? m lNVENTOR PURIFICATIUN OF BEET SUGAR SOLUTIONS Richard A. McGinnis, San Rafael; Calif., assignor to Spreckles Sugar- Company, San Francisco, Calif., a

This invention relates to improvements in the refining =of beet sugar solutions,- and more particularly to the removal of fioc-forming materials therefrom.

In the manufacture of heat sugar, the sugar is extracted from the raw beets with hotwater and the resulting solution' is treated with varioug' reagents such as lime and carbon dioxide toremovef a portion of the impurities from the solution. The solution is then filtered and concenitrated to around 55% sugar in multiple efiect evaporators. The'su'gar liquor'is then' boiled to grain, the crystals dried and otherwise treated to produce a final crystalline beet sugar product.

While beet sugar so produced attains a degree of purity of around 99.9%, itstill contains impurities in suflicient amount to be of serious concern to many consumers as well as the sugar manufacturer. The impurities which are particularly objectionableare minute qua'ntites of flocfor'ming materials which remain in the sugar liquors and in the sugarmade'therefrlornl e The presen'ceof floc-forming materialin beet sugar becomes apparent only whenthe crystalline sugar is dissolved in water andthe solutionaci'dified. On standing, the floc formin'g materials for a feathery solid or floc. The appearance-or formation of such flocculent precipirate has been the cause'of gre'a'tconcern to both the bottling industry and to' the sugar producers.

The fioc formed gives'an objectionable appearance to certain beverages and'isj thought to be responsible for some of the difiiculties encountered'inbev'era'g carbonation. syrup or beverage on standing. In' the'bottlingindustry, the presence of the flocin the bottlers products is un-' sightly and suggestiveof mold orbacteri'al contamination or'other undesirable impurities; The presence of minute traces of. flue-forming materials has seriously limited the sale of beet sugar products to the bottling industry. V

This fioc formation is a recognized problem, and studies havebee'n made of the nature of the fioc-formi'n'gmaterials and of methods" ofremovingflthem. See, for example, Flo'c in CarbonatdB evrageS, Industrial aiid Engineering Chemistry for 1952; vol; 44; pages 2844-2848. Proposals have been madefor the elimination of fiocforming materials by the addition to the beet sugar solutions of'carbonaceous adsorbents which are used once and are not regenerab'le, but' such proposals result in imperfect elimination of fioc, or are too expensive foreconomical operations.

The problem of floc rerrioval in beet sugar solutions is a different problem from that of d'colorization of the solutions. The coloring matter'in beet sugarsolutions as commonly producedisof a nature'such'thatspecial dcoloriz'a tion is not necssary-beforecrystallization"ofth sugar therefrom.

The flocculent precipitate forms in an acidified 'I'heproblem of'floc-reniovatfrombeet sugar solutions 2 amounting to a few parts per million, may result in objectionable floc formation when the sugar is used, e.-g., in carbonated beverages. 1:

The present invention provides an improvedprocess of effecting removal of floc-forming materials from beet:

sugar solutions, thus making the resulting beet sugar readily available in the bottling and other industries where the fioc problem has heretofore been a problem in the use of beet sugar. The improved process is not directed to the removal of color from beet sugar solutions. It is one advantage of the process that some color is removed, but this is incidental in amount and insufficient towarrant the practice of the process for color removing purposes. I

The improved process of the present invention also has the advantage that it does not result in the removal of ash from beet juices. And it is one of the advantages of the process that small amounts of ash constituents are retained which are beneficial in the use of the beet sugar, for example, for making hard candy, Where strength of the sugar is important and where the use of beet sugar has advantages over the use of cane sugar The improved process for the present invention is one in which the flee-containing beet sugar solutions are passed down through a series of stationary beds of an activated granular, regenerable, carbonaceous, fioc-forming'material-adsorbent, sufiicient in number so that removal of fioc-forming material is effected well before the sugar solution is discharged from the last bed, and with testing and control of the process to insure that there is a safe margin of travel of the solution through the last bed after the doc-forming materials have been removed.

The process of the present invention is based upon the discovery that the mechanism of the removal of fioc-forming materials requires, a different method of testing and control from that involved in the removal of other impurities such as color. Whereas the color or the concentration of other impurities of the effluent from a stationary bed'of the absorbent progressively increases as the flow of liquor continues, the floc-forming constituents of the liquor show a progressive removal until a critical point of essentially complete removal is reached, which is referred to as the break-through point. The breakthrough point may be defined as that point in the filter bed at which essentially all of the fioc-forming materials are removed, and beyond which the sugar solution is free from floc-forming materials,i.e., a zero fioc test as defined below. This break-through point progresses from the inlet to a bed to the outlet. And the process is controlled so that there is a safe portion of the last filter bed beyond the break-through point to insure that at no time will the break-through point reach the exit from the bed.

in the practical carrying out of the process with a series of filter beds, the first filter bed will be continued in operation until it becomes saturated or nearly so with doc-forming materials, so that it is no longer effective in removing such constituents. And this bed is then re* moved. A suflicient number of other beds is maintained on stream so that, when the first bed is thus saturated with doc-forming materials, the break-through point will be a safe margin from the exit of thelast filter bed. And before the break-through point reaches the dischargeof the last filter bed, a new filter bed is added to insure that at no time does the break-through point reach the exit from the final bed. There is thus provided a safe margin of removal activity, beyond the break-through point, to in sure that the effluent is essentially free from flee-forming materials.

In order'to insure proper control of the process, it is impossible to test the elfiuent, as is customary in the use of a series of filter beds for decolorizing purposes. It is necessary that the testing procedure be applied to samples taken from the filter beds at different stages to determine where the break-through point is, within limits, and to insure an adequate removal activity beyond the break-through point.

The determination of the presence or absence of flocforming materials in any given beet sugar solution is not a simple one. Tests for floc which can be quickly made may give a rough indication, but cannot be correlated with the fioc content of the sugar boiled from the liquors. Accordingly, the testing of the liquors themselves is not entirely reliable. It is necessary to boil sugar from the liquors and to dissolve the sugar and test the resulting sugar solution. And this is a time-consuming operation. Nevertheless, by the making of proper tests in connection with the operation of the process, the rate of travel of the break-through point can be determined with sufficient approximation to enable a safe margin of fiow of the sugar solution through the last filter bed between the break-through point and the effluent from this bed. This is in marked contrast with the testing of effluent sugar solutions for color, which can readily be made by comparison with standard color solutions by the eye or by instruments in a matter of a few minutes. This testing of the effluent is not possbile in testing for floc removal or the presence of floc-forming material. Thus, the determination of the presence or absence of floc-forming materials in any given beet sugar solution, or in the solution at any stage of its passage through the filter beds, can only be truly established by boiling strikes of crystalline sugar from the liquors, centrifuging off the crystals, drying the same and testing the solutions made from these crystalline sugars for flocformation after acidification to pH values approaching or below about 2.5. Heat has been found to hasten the process of floc formation.

Since the floc-forming materials are present in sugar to an extremely minute extent, measured in parts per million, one difficulty has been to obtain an evaluation of the extent of their presence. The following test has been established to show not only the presence or absence of floc-forming materials in the solid sugar, but also to provide a method of grading their relative concentrations of the floc-forming material.

The following procedure has been found to work satisfactorllyz (1) Place 70 grams of the sugar to be tested in an 8 oz. bottle. Use round, medium tall, wide mouth flint glass bottle with molded screw cap and a Vinylite iner. perature and stir to dissolve the sugar. (3) Acidify to 2 pH with C.P. phosphoric acid. (4) Fit cap loosely on the bottle and place bottle in a briskly boiling distilled water bath equipped with a close fitting cover and continue boiling for 15 minutes with bath covered. A 1 /2 quart Revere Ware kettle with lid has been found to make a suitable bath. (5) At the end of 15 minutes time in the boiling water bath, remove bottle and tighten the cap and set aside for observation. Do not shake or disturb sample after placing aside for observation. (6) Inspect for floc after 4 hours and 24 hours. Observations are made by shining a strong pencil beam of light through the solution towards the observer. An American Optical Co. No. 353 Universal microscope illuminator or equiva lent has been found to be suitable.

The flocculating tendency is rated as follows:

0, when no floc is visible at 24 hours.

1, when light floc is visible after 24 hours but none after 4 hours.

2, when heavy floc is visible after M hours but none after 4 hours.

3, when light floc is visible after 4 hours.

4, when heavy floc is visible after 4 hours.

It has been found that only sugars with a fiocculating tendency rating of 0 will be suitable for the bottling trade as floc-free sugars, and one object of this invention is to provide a process to produce such sugars.

(2) Add 163 ml. of distilled water at room temuse in the bottling industry and is, for practical purposes,-

a floc-free sugar.

It is recognized that the thirty-odd hours which it isnecessary to wait to determine whether the effluent sugar solution from the treatment is free from floc poses a serious control problem in order to produce floc-free sugar. Nevertheless, by making a series of such tests of sugar solution drawn from diiferent portions of each of the filters, it is possible to provide a general operating guide and to determine the approximate beds where the filter bed has become saturated or nearly so with floc materials and the decreased amounts at intermediate stages and the break-through point beyond which no floc-forming materials are present, so that a sufiicient margin of flow path beyond the break-through point can be obtained before the sugar solution leaves the last filter. Such a general operating guide enables one to obtain floc-free sugar by the simple filtration of beet sugar liquors downwardly through a series of beds of the activated adsorbent granular carbon, so that the carbon can be used to its maximum efiiciency and complete freedom of the effluent from flocforming materials obtained.

Thus, with flow rates of about one half gallon of standard sugar solution or thick juices per square foot of filter area per minute, up to about two gallons per square foot per minute, it has been established that the bed depth of the granular carbon necessary to obtain a flocculation tendency rating of zero, by the method above described, is of the order of 30 to 35 feet of filter bed from the feed point or from the point ofsaturation with floc-forming materials to the break-through point. This bed depth may vary to some extent in practice, but in general it has been found that one should provide at least this order of bed depth between the point of saturation of the granular carbon with respect to floc-forming materials and the efiluent point where the floc-free sugar is to be expected.

Under these circumstances, it has been found that from around 100 to 200 pounds of floc-free sugar can be obtained from standard beet sugar liquor per pound of carbon, depending on the temperature. For the most efficient operation, the maintainence of a maximum bed depth of carbon between the saturation point and the expected floc-free effluent point is necessary, with a margin of flow of the sugar solution beyond the break-through point and before reaching the efiluent point.

The beet sugar solutions are passed through the filter beds at elevated temperatures of around 70-96 C., and advantageously in the range of -96 C., which results in better operation of the process than lower temperatures in the 70 range. The temperature of the sugar solution is maintained by heating the sugar solution before it enters the filter beds and by providing insulation or heating means such as heating jackets on the filters to maintain the desired temperature of the liquor passing therethrough.

Considering the removal of floc-forming materials as one of the steps or operations in the process of preparing sugar from sugar beets, it should be recognized that the liquors, after such treatment, and the sugars subsequently boiled from these liquors will be floc-free, provided the process has been properly carried out and without bypassing or contamination of the floc-free liquor with other liquors. In other words, the removal of floc is at a stage of the process prior to which the sugar solutions contain floc-forming materials and after which the sugar solutions are free from floc-forming materials, provided there is no bypass of untreated liquor or contamination of treated liquor with other liquors.

While the process may be applied to thin beet sugar liquor, it is more advantageous to apply it to the thick juices from the evaporators,'or the standard'liqnor con:

solution made by remelting some of the sugar products subsequently formed in the process.

The granular adsorbent carbonaceous material is a regenerable carbonaceous material such as is obtainable from coal and such as has heretofore been proposed for use in' the decolorizing of corn and other sugar solutions (see U.S. Patents Nos. 2,763,580 and 2,823,304). The activated granular carbon can thus be made by briquetting powdered anthracite coal with a coal tar binder, granulating the briquets to the desired size, and calcining in a furnace at around 900 C. in the presence of controlled amounts of steam and air for activation. Such granular carbon has the advantage that it can be'regem erated by recalcining.

The carbon which has been found well suited for use is the carbon available on the market as Pittsburgh granular activated carbon-type CAL, obtainable from Pittsburgh Coke & Chemical Corporation, and having the following properties:

Apparent density Total surface-(N BET method), In. /g1. 1000-lieu Mesh size U.S. sieve (with not more than 5 over 12 mesh or below 40'mesh) 12 x 40 Mean particle diameter, mm 0.90-1.10 Iodine number, minimum 1000 Molasses number, minimum 230 Ash, maximum, percent 8.5 Moisture as packed, maximum, percent---" 2.0 Abrasion number, minimum 75 It has sometimes been found advantageous to use such a granular carbon in conjunction with some means of pH regulation such as by the addition of up to usually about 5% by weight, of dead-burned magnesite, to reduce the tendency of the granular carbon to lower the pH of the sugar liquor to a point where inversion of sucrose becomes objectionable.

In the practice of the invention with maximum efliciency of the use of the granular carbon, it is essential to use a plurality of beds in series with a sufiicient length of travel of the sugar solution through the successive beds so as to effect practically complete saturation of the first bed with the flee-forming material, and to maintain a sufiicient length of travel to insure that the break-through point does not reach the efiiuent point from the last filter. And in order to avoid too close an approach of the breakthrough point to the eifiuent, it is important to add another filter bed well before the break-through point reaches the efiiuent.

The invention will be further described in connection with the accompanying drawings, which illustrate, in a somewhat conventional and diagrammatic manner, an arrangement of filter beds, but it will be understood that the invention is not limited thereto.

In the accompanying drawings,

Fig. 1 shows a series of six filter beds, of which four are in operation; and

Fig. 2 shows the same number of filter beds at a subsequent stage of the operation.

Each of the filter beds is about 8 feet in diameter and 16 feet high, and each contains about 20,000 pounds of the decolorizing adsorbent granular carbon above refferred to. Of the six filters", 2', 3, 4 andSareconnected in series with the sugar solution tobe' treated entering the top of filter bed 2 and'the sugar solution passing'from the bottom of this bed to the top of filter bed 3, and .so

' on tofilter bed 5, fromwhichthe solution free from flocforming material, is removed as the effluent; I

Each filter has'a valve-controlled inlet pipe 7, a valvecontrolled outlet pipe 8, and valve-controlled sample lines 9 at different levels of the' filter beds.

Filter bed 1 has been removed fromthe series with the granular carbon saturated or practically saturated with floc-form-ing materials. The point of saturation will progress downwardly through the'zfilter bed 2, and the break-through point will progress downwardly through filter bed 4, or into the top of filter bed 5. When filter bed 2 becomes saturated with floc material, the break-through point Will be some distance from the effiuent from filter bed 5.

Filter bed 1 illustrates the filter bed which has been saturated with fioc-forming material and removed from the series. In normal operation, water will be passed down through thisbed todisplace the sugar solution, the sugar removed will make sweet water, and the granular carbon will be passed to the regenerating apparatus indicated at 10, and thenpassed to storage or to the filter bed 6, which is charged with regenerated carbon or a mixture of regenerated' and fresh carbon and is thus made ready to add to the serieswhen filter bed No. 2 becomes saturated and is removed and before the break-through point reaches the bottom of column 5. The connections 11' and 12 lead from and to theregenerating apparatus 10'.

Fig; 2 shows a later stage of the operation, where filter bed 2 has beensaturatedwith floc-forming material and removed from-the series; and filter-bed 6 has been: added to the'seriesr Filter bed-2 is 'then-treated'to remove sugar solution from the carbon, and the carbon is regenerated and returned to filter bed 1, which is then added to the series, taking the effluent from filter bed 6 when filter bed. 3 becomes saturated and is removed.

As an illustration of the carrying out of the process, each filter bed may remain in operation approximately 144 hours or 6 days, with 4 filter beds continuously in operation, one filter bed being removed and the carbon therefrom regenerated, and another filter bed being prepared for adding to the system the following day.

Each filter bed, as it is removed from the system on successive days or at successive intervals, will have the sugar solution removed therefrom by displacement with water, and the carbon will then be washed and removed from the filter and sent to, the regenerating apparatus, where it will be dried and regenerated or reactivated, e.g., in a rotary calcining kiln or a multi-hearth furnace such as a Herreshoff furnace or similar device. The regenerated or reactivated granular carbon, either without or with addition of fresh granular carbon, is then stored or returned to the empty filter to form a new filter bed. When the new filter bed is thus prepared, it is ready for adding to the system to replace the filter bed which has become saturated with floc-forming material.

In addition to effecting removal of floc-forming materials, the present process has the advantage of accomplishing a partial reduction in color as Well as a reduction of certain other impurities. However, the reduction in color is not such as would make the process a decolorizing process in the ordinary sense, and it is not controlled from the standpoint of color removal. The partial removal of color, While advantageous, is incidental and insufficient to warrant the practice of the process for color removal purposes.

It is one advantage of the process that the complete removal of fioc is accomplished without removal of small amounts of'inorganic or ash constituents which are desirably left in the fioc-free sugar.

The beet sugar solutions which can be treated according to the present process include both thick or concentrated sugar solutions and standard liquors. The treatment results in the production of an improved beet sugar product which is free from objectionable floc-forming constituents, which retains its small amount of desirable inorganic constituents, which is somewhat reduced in color constituents, and which is available for use to advantage as an improved beet sugar product, giving a fioc-free sugar for use in the bottling industry and a fioc-free and mineral-containing sugar for use in the hard candy industry.

I claim:

1. A method of treating beet sugar solutions containing flee-forming materials which comprises passing the same through a series of beds of granular, flee-formingmaterial-adsorbent carbon with progressive removal of fioc-forming constituents from the sugar solution passing therethrough taking samples from the filter beds at different stages to determine the breakthrough point beyond which the sugar solution is free from fioc-forrning materials and the rate of travel of the breakthrough point in the filter beds, and maintaining a sufficient depth of the filter bed between the breakthrough point and the efiluent to insure removal of floc-forming materials at a point in advance of the discharge of the solution from the last filter bed.

2. The method of treating beet sugar solutions to remove flee-forming constituents therefrom which comprises passing the solution through a number of filter beds of granular floc-forming-material-adsorbent carbon arranged in series with a sufiicient length of travel of the solution through the filter bed to enable the first filter bed to become substantially saturated with fioc-forming materials before it is removed from the series, taking samples from the later filter beds of the series at difierent stages to determine the breakthrough point beyond which the sugar solution is free from floc-forming materials and the rate of travel of the breakthrough point in the later filter beds, and adding a fresh filter bed to the series after the breakthrough point reaches the exit of the next preceding filter bed of the series to insure removal of fioc-forming materials at a point in advance of the discharge of the solution from the last filter bed of the series.

3. The method of purifying beet sugar solutions containing doc-forming materials which comprises passing the sugar solution successively through a series of stationary filter beds containing granular floc-forming-material-adsorbent carbon, predetermining the length of travel of the sugar solution through the filter beds at which complete elimination of flee-forming materials has occurred by taking samples from the filter beds at diiferent stages to determine the breakthrough point of complete removal of flee-forming materials and the rate of travel of the breakthrough point in the filter beds, and maintaining a suflicient number of filter beds to insure that the breakthrough point of complete removal of fioc is well in advance of the efirluent point from the last filter.

References Cited in the file of this patent UNITED STATES PATENTS 2,763,520 Zabor Sept. 18, 1956 2,822,304 Gillmore Feb. 4, 1958 FOREIGN PATENTS 641,992 Great Britain Aug. 23, 1950 OTHER REFERENCES Beet Sugar Technology; by McGinnis, 1951, pp. 278, 279, and 283-289.

Sugar, March 1952, pp. 35-38.

UNITED STATES PATENT OFFICE CERTIFICATION OF COECTION Patent Noo 2 9619 298 January 24 1961 Richard A McGinnis It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below'.

Column 2, line 23, for "for" read of column 8, line 4, for "after" read before --=-Q Signed and sealed this 13th day of June 19610 7 (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LAD-D Attesting Officer Commissioner of Patents 

1. A METHOD OF TREATING BEET SUGAR SOLUTIONS CONTAINING FLOC-FORMING MATERIALS WHICH COMPRISES PASSING THE SAME THROUGH A SERIES OF BEDS OF GRANULAR, FLOC-FORMINGMATERIA-ADSORBENT CARBON WITH PROGRESSIVE REMOVAL OF FLOC-FORMING CONSTITUENTS FROM THE SUGAR SOLUTION PASSING THERETHROUGH TAKING SAMPLES FROM THE FILTER BEDS AT DIFFERENT STAGES TO DETERMINE THE BREAKTHROUGH POINT BEYOND WHICH THE SUGAR SOLUTION IS FREE FROM FLOC-FORMING MATERIALS AND THE RATE OF TRAVEL OF THE BREAKTHROUGH POINT IN THE FILTER BEDS, AND MAINTAINING A SUFFICIENT DEPTH OF THE FILTER BED BETWEEN THE BREAKTHROUGH POINT AND THE EFFLUENT TO INSURE REMOVAL OF FLOC-FORMING MATERIALS AT A POINT IN ADVANCE OF THE DISCHARGE OF THE SOLUTION FROM THE LAST FILTER BED. 